With RED being S35, when you use the 150-600, which as you know is designed to cover FF35, you're shooting a crop out of the center of the lens. With the 2x on the 150-600 the minimum aperture is f11 so you need a ton of light - usually much more than you get in "magic hour" shooting. I've never thought the 150-600 is good wide open. I prefer it between f8 and f11 - as you know its the sweet spot of the lens.
The solid state drives (RED RAM) are quite good - but at $4,500 USD per drive they are costly. If you'll be getting excessive bounce while shooting you may want to go for the RED RAM drives. Maybe a combo of some RED RAM drives and some regular RED Drives with ET Shock Mounts would be the best idea.
For backup in the field we've been using duplicate 1 TB hard drives. My Book Studio Edition, with dual FireWire 800 buses have been very dependable for us - plus they're pretty small, thus easier to cart around. We put them in zippered protective cases from Western Digital for traveling. We're also looking for a small mobile LTO datatape solution, so we can back up to one drive, and then one LTO tape in the field. It sounds like you won't have a lot of backing up to do, so no, I don't think you need a separate data wrangler. With a MacBook Pro to check the RED Quicktime dailies, and Firewire 800 buses on the MacBook and the portable drives, the backing up goes real fast after the days shooting - with the amount of daily footage you said you'll have.
I got your PM. A short while ago I sent you of an email reply.